1. Field of the Invention
This technology relates to phase change memory cells.
2. Description of Related Art
Phase change memory cells degrade with continued regular operation. It is believed that the degradation is caused by the flow of current through the phase change memory cell. A result of degradation is that, the resistance of the amorphous state decreases and the resistance of the crystalline state decreases.
In application Ser. No. 12/286,874, a mesh of phase change material and dielectric material is formed to control the formation of particular crystalline phases of phase change material. Such controlled formation of particular crystalline phases limits the volume of phase change material which undergoes the change between the amorphous state and the crystalline state. Nevertheless, this volume continues to undergo stress. This shares a common feature of many memory algorithms that adjust the operation of a phase change memory array once, and then continue without adjustment thereafter during regular operation of the phase change memory array.
Memory verify algorithms generally adjust the operation of a phase change memory array, upon a demonstrated failure of the phase change memory array. However, it is costly in time and throughput to rely on such demonstrated failure before every algorithm adjustment, particularly if the cause of the failure is widespread among many memory cells in an array, rather than limited to only a small number of memory cells in an array.